The invention is in the field of starch derivatives, and more particularly, is in the field of derivatized malto-oligosaccharides. The derivatized malto-oligosaccharides of the invention find particular utility as trash scavengers in the pulp and paper industry.
In papermaking furnishes, anionic trash, which includes such materials as lignins, hemicelluloses, and fatty acids, is common. This trash material interferes with the performance of other additives, which include cationic retention aids, starches, and sizing agents, and often causes a reduction in machine performance and in physical sheet properties. To reduce the amount of anionic trash in the furnish, the prior art has taught to add a coagulant (commonly known as a xe2x80x9ctrash scavengerxe2x80x9d) to the papermaking furnish at the wet end of the papermaking machine. The coagulant carries a cationic charge in solution, and tends to neutralize the an ionic trash material, keeping it from interfering with the performance of other process aids, and allowing it to be removed from the process with the fiber as the sheet is formed. Commonly used coagulants include alum, polyaluminum chloride (PAC), polyethylenimine, polyamines, and poly diallyldimethyl ammonium chloride (poly DADMAC).
Charged starches may be used as trash scavengers in connection with the treatment of pulp and paper process water. In many such applications, it is desired to derivatize starch or derivatives of starch (such as maltodextrins) to impart a charge to the starch backbone. Many methods for derivatizing starch and starch derivatives are known. For example, U.S. Pat. No. 5,795,397 (Shi et al., assignors to National Starch and Chemical Investment Holding Corporation, Wilmington, Del.) purports to disclose enzymatic treatment of starch derivatives to form modified starch derivatives. The modified starch derivatives are said to be useful as an ingredient in remoistenable adhesive compositions. The starch derivatives taught by this patent generally have a degree of substitution (DS) less than about 0.5, and thus generally are not suitable for use in applications where a higher DS starch is desired. Another document, WO095/18157 (Vihervaara et al., assignors to Raisio Chemicals Oy, Raisio, Finland), discloses starch derivatives that have a higher degree of substitution than those taught in U.S. Pat. No. 5,795,397. It has been found difficult, however, to reproduce the teachings of this patent; moreover, there remains room for improvement of the coagulants described therein.
It has now been found that malto-oligosaccharides can be derivatized in an aqueous medium with cationic derivatizing agents to form derivatized malto-oligosaccharides. It has further been disclosed that such derivatized malto-oligosaccharides are useful as trash scavengers in the pulp and paper industries.
In accordance with one embodiment of the invention, a method for derivatizing malto-oligosaccharides is provided. The invention contemplates a method wherein a malto-oligosaccharide is derivatized in aqueous medium with a cationic agent to form a derivatized malto-oligosaccharide having a DS greater than about 0.5, or, when the derivatized malto-oligosaccharide is used as a coagulant, derivatized to any, DS sufficient to render the derivatized malto-oligosaccharide suitable for use as a trash scavenger. The invention further encompasses a method for trash scavenging. The trash scavenging method includes the steps of providing a liquid that contains anionic materials, and adding to the liquid an amount of the derivatized malto-oligosaccharide effective to neutralize at least a portion of the anionic materials. The method preferably is utilized in connection with the manufacture of paper. The invention also encompasses a process for preparing a paper web, as well as a paper web prepared in accordance with the inventive process. In accordance with these embodiments, a furnish that contains anionic materials is provided. The anionic material is neutralized using a cationically derivatized malto-oligosaccharide.